Rendering porous structures impermeable by treatment with pH insensitive gelable compositions of amide polymers and composition

ABSTRACT

Aqueous solutions of amide polymers, such as polyacrylamide when treated with small amounts of a water-soluble polyaldehyde and a hypohalite salt at an alkaline pH, react to form firm gels within a short time at ambient temperature. Such gels, which are stable under alkaline as well as acidic conditions, are usefully employed to plug porous subterranean formations, for grouting of leaking soil pipes or wells, and to otherwise render porous structures impermeable to the passage of liquids such as water.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of Serial No. 911,863, now U.S. Pat.No. 4,199,625 issued Apr. 22, 1980.

BACKGROUND OF THE INVENTION

This invention relates to the rendering of porous structures impermeableto passage of liquid such as water by treating such porous structureswith an aqueous gelable composition containing an amide polymer.

Soil stabilization and grouting have previously been accomplished byforming an aqueous gel in the unstable soil as shown, for example, inU.S. Pat. Nos. 2,856,380 and 2,940,729 wherein a solution containing anethylenically unsaturated monomer together with a crosslinking monomersuch as methylene bis-(acrylamide) is pumped into the ground and therepolymerized in situ to form a crosslinked gel. Unfortunately, this priorart procedure not only exposes the operator to toxic monomers such asacrylamide but has been found on occasion to allow such toxic monomersto escape polymerization and thereby permeate into the soil water intoxic form. As a result, otherwise potable water sources are endangered.

Preformed, lightly crosslinked polymers and copolymers of acrylamidehave been suggested as sorbents or gelling agents for aqueous fluids,for example, in U.S. Pat. Nos. 3,520,925 and 3,810,468. However, thepreparation of such polymers or copolymers is very expensive. Moreimportantly, insofar as the use of such pre-crosslinked polymers in soiltreating applications are concerned, such polymers are not readilyadapted to be pumped into porous soil, cracks in sewers or similarporous structures.

In view of the deficiencies of prior art methods for treating porousstructures with polymeric materials to render them impermeable topassage of liquids such as water, it would be highly desirable toprovide an improved method for so treating porous structures whereby thepolymer to be employed is readily pumped into or otherwise incorporatedin the porous structure to be rendered impermeable without polluting theporous structure and its surrounding environment with toxic substances.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a method for rendering porousstuctures impermeable to the passage of liquids by treating them with anaqueous gelable reaction mixture comprising a water-soluble orwater-dispersible aliphatic polyaldehyde, a hypohalite salt and awater-soluble polymer derived from an ethylenically unsaturated amidewherein the polymer, the hypohalite salt and the polyaldehyde arepresent in proportions and under conditions of temperature and alkalinepH sufficient to form a gel capable of rendering the porous structureimpermeable.

In another aspect, this invention is an aqueous gelable reaction mixturecomprising the aforementioned water-soluble amide polymer, polyaldehydeand hypohalite salt in proportion sufficient to cause the mixture toform an alkali-stable water-insoluble gel when the mixture is subjectedto gelation conditions.

An embodiment of particular interest involves placing the aforementionedgelable composition in a porous subterranean formation and subsequentlygelling the composition to render the formation impermeable. In asimilar embodiment of interest, the gelable composition is pumped orotherwise forced into cracks or similar porosities in sewer pipes,potable water wells and like conduits and then gelled in place therebyplugging and thereby alleviating leakage from or into the conduits. Thislatter embodiment is hereinafter referred to as "grouting of porousstructures."

It is among the advantages of the invention that water-insoluble gels,preferably those that are also firm, non-weeping, structurally sturdyand liquid impervious, are obtained from the gelable compositionsemployed in the practice of the present invention. It is a furtheradvantage of the invention that the gelation reaction is initiatedwithin a controlled reasonable period of time after the amide polymer,the hypohalite salt and the aliphatic polyaldehyde, preferablydialdehyde, are contacted in an aqueous medium having the propercontrolled alkaline pH. Such gelation reaction proceeds readily atambient or higher temperatures.

It is indeed surprising that the method of the present inventionprovides a firm gel capable of rendering a porous substrate impermeable.It is even more surprising that such gel, which forms very rapidly atalkaline pH, is very stable in both alkaline and acidic environments.

In addition to the aforementioned utilities of the present invention,the compositions employed in the present invention may also be employedin such applications as blocking off seepage under buildings orhighways, preventing seepage loss through dams, dikes and irrigationditches, blocking infiltration of polluted ground water into potablewater wells or to replace aqueous gels prepared from gelatine orvegetable gums as, for example, in air-freshener devices or in gelledcosmetics such as roll-on deodorants and the like.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The amide polymers employed in the practice of this invention havepolyethylenic backbones bearing pendant carboxamide moieties. Such amidepolymers are normally addition polymers containing polymerizedethylenically unsaturated carboxamide monomers which may contain up to50 mole percent of another ethylenically unsaturated monomercopolymerizable with the carboxamide monomer or monomers. So long as theamide polymer has sufficient molecular weight to react with thepolyaldehyde and hypohalite salt to form a desired firm gel, molecularweight of the amide polymer is not particularly critical. The viscosityof an aqueous solution of the amide polymer is an index of the molecularweight of said polymer and, thus, for most of the purposes of thepresent invention it is desirable to employ polymers of relatively lowmolecular weight so that a substantial proportion of solids can beincorporated in the aqueous solution of polymer without producingexcessive viscosity such as to render the solution diffficult orimpossible to pump. Gelation in accordance with the invention can beobtained with amide polymers having such low molecular weights as to becharacterized by a viscosity of only about 50 centipoises for an aqueous40 percent by weight solution of the polymer. On the other hand,gelation can be obtained with amide polymers of very high molecularweight characterized, for example, by a viscosity of 60 centipoises foran aqueous 0.2 percent by weight solution thereof. In practice, toprovide the firmness, abrasion resistance and structural stabilitydesired in gels employed for plugging porous structures, as, forexample, in and around sewer pipes, it is preferred to produce a gelcontaining from about 5 to 10 percent or more of amide polymer solids.Thus, for ease of handling and placing in the porous structure, it ispreferred to employ amide polymers characterized by viscosities of fromabout 100 centipoises to about 15,000 centipoises for an aqueous 20percent by weight solution thereof.

To form the desired gel capable of rendering the porous structureimpermeable, the amide polymer preferably contains from about 50 to 100mole percent of one or more ethylenically unsaturated carboxamidemonomers, more preferably from about 70 to about 100 mole percent, andmost preferably from about 90 to about 100 mole percent of amidemonomers. Exemplary carboxamide monomers include acrylamide,methacrylamide, fumaramide, ethacrylamide, N-methylacrylamide and thelike. It is understood that the finished polymer contains sufficientwater-solvating carboxamide moieties to render the finished polymersoluble in water to the extent of at least 5 percent by weight andpreferably to the extent of 20 percent or more by weight. Acrylamide,per se, is the preferred carboxamide monomer.

Examples of other monomers which may be copolymerized with theaforementioned amide monomers and which do not generally interfere withthe gelation reaction include unsaturated aliphatic acids such asacrylic and methacrylic acid, and their water-soluble salts,particularly alkali metal salts, such as sodium acrylate or sodiummethacrylate; hydroxy alkyl and alkyl esters of α,β-ethylenicallyunsaturated carboxylic acids such as ethyl acrylate, methyl acrylate,butyl acrylate, methyl methacrylate, hydroxyethyl acrylate; sulfoalkylesters of α,β-ethylenically unsaturated carboxylic acids such assulfoethyl acrylate and the sodium salt thereof, vinylbenzyl chlorideand vinyl benzyl quaternary ammonium halides such as vinyl benzyltrimethyl ammonium chloride; isopropenyl oxazoline; monovinylidenearomatics and sulfonated monovinylidene aromatics such as styrene andsodium styrenesulfonate. Of course, it is understood that said othermonomers should also be chosen so that they do not react with the amidemonomer or otherwise interfere with the gelation reaction. Amidepolymers are sometimes subject to some degree of hydrolysis duringpreparation or may purposely have a proportion of their amide groupshydrolyzed to carboxylate groups during or after preparation. For thepurposes of this invention such partially hydrolyzed amide polymers areequivalent to the corresponding copolymers of carboxamide monomer andunsaturated aliphatic acid salt.

Also included within suitable amide polymers are graft polymers whereinthe amide monomers or other suitable monomers are grafted on cellulosicpolymers such as cellulose, methylated cellulose and hydroxypropylmethylcellulose.

In general, any aliphatic polyaldehyde, having sufficient solubility ordispersibility in water to enable rapid, intimate mixing with an aqueoussolution of amide polymer, may be employed in the method of the presentinvention. In practice, saturated aliphatic polyaldehydes are preferred.Suitable polyaldehydes include dialdehydes, such as glyoxal,succinaldehyde, glutaraldehyde and the like, as well as more complexchemicals such as water-soluble or water-dispersible polyaldehyde starchderivatives. For most purposes a dialdehyde, particularly glyoxal, ispreferred.

The hypohalite salt is suitably any metal hypohalite, but is preferablyan alkali metal hypochlorite or hypobromite, most preferably sodium orpotassium hypochlorite.

In practicing the method of this invention, it is only necessary thatthe amide polymer, hypohalite salt and the polyaldehyde be thoroughlymixed in the proper proportions in an aqueous medium under conditions ofsuitable alkalinity to provide a gelable aqueous reaction mixture. Onesuch procedure is carried out by thoroughly mixing an aqueous solutionof the hypohalite salt with an aqueous solution of the amide polymer andthe polyaldehyde under proper alkaline conditions. Alternatively, anaqueous solution of polyaldehyde is mixed with an aqueous solution ofamide polymer and hypohalite salt under proper alkaline conditions.

In the gelable aqueous reaction mixture, the concentration of the amidepolymer varies depending upon the molecular weight of the polymer andthe firmness of the gel desired. If the amide polymer has a relativelylow molecular weight, the concentration of amide polymer isadvantageously from about 0.25 to about 30, preferably from about 3 toabout 20, most preferably from about 5 to about 15, weight percent basedon the reaction mixture. For the purposes of this invention, an amidepolymer has a relatively low molecular weight if a 40 weight percentaqueous solution of the polymer exhibits a viscosity in the range fromabout 50 to about 15,000 centipoises as determined by a Brookfield LVTviscometer (#2 spindle, 15 rpm, 25° C.). It is understood, however, thatsomewhat lower concentrations than the aforementioned can be employedwith higher molecular weight amide polymers.

The concentration of polyaldehyde in the gelable reaction mixture is atleast an amount sufficient to cause the reaction mixture to form awater-insoluble, three dimensional gel within 5 minutes after themixture is subjected to gelation conditions, up to the saturationconcentration of the polyaldehyde in the reaction mixture.Advantageously, however, the gelable reaction mixture contains enoughpolyaldehyde to provide from about 1 to about 300, preferably from about5 to about 100, millimoles of aldehyde moiety per mole of carboxamidemoiety ##STR1## in the amide polymer. When the polyaldehyde is glyoxal,the concentrations of glyoxal sufficient to provide the aforementionedmole ratios are within the range from about 0.004 to about 1.2,preferably from about 0.02 to about 0.4, weight percent based on thegelable reaction mixture. For sewer grouting and similar subterraneanplugging applications, it is preferred to employ from about 15 to 60millimoles of polyaldehyde per mole of carboxamide moiety in the amidepolymer.

The concentration of the hypohalite salt in the gelable reaction mixtureis an amount sufficient to provide the resulting gel with alkalinestability. A gel possesses the requisite alkaline stability if it doesnot dissolve in an aqueous medium having a pH of 8 in a period of atleast a week after the gel is placed in the aqueous medium. Gels havingpreferred alkaline stability do not dissolve in an aqueous medium havinga pH of 8-10 for a period of six months, those gels which are insolublein 5 N NaOH for a week being most preferred. The concentration ofhypohalite salt is in the range from about 2 to about 600, preferablyfrom about 10 to about 250, most preferably from about 15 to about 160millimoles of the hypohalite anion per mole of carboxamide moiety in theamide polymer. The hypohalite salt is advantageously employed in theform of an aqueous solution prepared by dissolving the correspondingfree halogen in a slight molar excess of alkali metal hydroxide or otherrelatively strong base with cooling to prevent the formation of halitesor halates. As a result of this preferred practice, a solution is madewhich contains a mole of halide ion for each mole of hypohalite ionformed. A slight excess of the base is beneficially employed tostabilize the hypohalite solution and to provide an aqueous solution ofhypohalite having a pH of at least about 12 and preferably a pH over 13without containing such an excess of alkali as to cause undesiredhydrolysis of the amide groups of the polymer when the hypohalitesolution is mixed with the amide polymer solution. For economicalreasons, it is desirable to employ a commercial household bleach whichis an aqueous solution containing about 5.25 to 5.5 weight percent ofsodium hypochlorite, an approximately equimolar proportion of sodiumchloride and sufficient excess of sodium hydroxide to provide a solutionhaving a pH of 13.5 or slightly higher. In commercial bleach thestabilizing excess of NaOH corresponds to about 0.3 to 1 percent byweight of the solution.

Advantageously, the pH of the reaction mixture at the initiation ofgelation should be at least 7.5 up to 14, preferably from about 8 toabout 13.5, most preferably from about 10 to about 13. This desiredalkalinity at the outset of gelation is accomplished by the addition ofa relatively strong base to one of the aforementioned startingingredients, preferably the polyaldehyde and/or the hypohalite salt,most preferably the hypohalite salt, or to the reaction mixture prior togelation. Generally any base capable of generating the needed alkalinepH which does not interfere with the gelation reaction is usefullyemployed. Examples of relatively strong bases advantageously employed toprovide this desired alkalinity include alkali metal hydroxides such assodium and potassium hydroxide; metal phosphates such as trisodiumphosphate; metal carbonates such as sodium carbonate; alkylamines suchas dimethylamine, methylamine and trimethylamine; and other organicbases such as ethylenediamine. Of the foregoing bases, those such astrisodium phosphate which provide a maximum pH in the range from about 9to about 14 are preferred.

In practice, when operating temperatures from about 20° C. up to atemperature at which the amide polymer or other reactants degradeprematurely, the gelation reaction is initiated rapidly when an aqueoussolution of the amide polymer and polyaldehyde is brought together withthe hypohalite salt dissolved in the alkaline solution, particularlywhen the reaction mixture has a pH in the preferred pH range from about10 to about 13. Thus, for example, when an aqueouspolyacrylamide/glyoxal solution at a pH below 7 and at a temperaturefrom about 20° C. to 25° C. is combined with an aqueous solution ofsodium hypochlorite containing sufficient trisodium phosphate so thatthe pH of the resulting reaction mixture is in the range from about 10to about 13.5, the resulting mixture sets to a firm water-insoluble gelwithin a matter of seconds while the pH falls to a value within therange of 7 to 11. It will be apparent to the skilled artisan that a widerange of gel times can be obtained with any particular mixture of amidepolymer, hypohalite salt and polyaldehyde by suitable adjustment of thetemperature or pH or both. Although less preferred than the gels made bythe foregoing technique, suitable gels can be formed by first reactingthe polyaldehyde with amide polymer and then contacting this gelreaction product with the hypohalite salt.

The amide polymer solutions employed may be prepared by known methods.Thus, for example, an amide monomer or monomer mixture as defined abovemay be dissolved in water and subjected to catalytic solutionpolymerization by addition thereto of a redox catalyst system such as aperoxide-bisulfite system or by the use of a peroxide or azo catalystwith controlled heating. Alternatively, the polymer may be prepared byknown methods, e.g., U.S. Pat. No. 3,284,393, as a water-in-oilsuspension or emulsion in a water-insoluble liquid such as a liquidhydrocarbon and the desired polymer solution be prepared by invertingsaid emulsion or solution in water, for example, with the aid of asurfactant. It is further understood that the amide polymer may be driedand then redissolved in an aqueous medium to form a suitable aqueoussolution.

In the practice of the invention, it is generally necessary to providemeans for placing the gelable reaction mixture in the position desiredbefore gelation occurs. Thus, for example, an aqueous solution of theamide polymer and polyaldehyde and an alkaline solution of thehypohalite salt may be pumped by separate pipe systems and mixed at (orimmediately adjacent to) the site where it is desired to deposit thegel. In the plugging of porous subterranean strata, as when undesiredseepage is polluting a water well, packers can be placed above and belowthe porous strata. The amide polymer/polyaldehyde solution and alkalinehypohalite solution can then be introduced into the space between thepackers through separate pipes whereby the solutions are mixed in saidspace and forced under pressure into the porous formation where gelationprovides the desired plugging.

When a crack or perforated area is detected in a sewer pipe or wellcasing, for example, by remote television survey or other pipe or welllogging method, it is convenient to employ a packer having endpieceswhich can be inflated hydraulically to provide positive pressure sealson either side of the cracked or perforated area, said endpieces beingconnected by a cylindrical member of somewhat smaller diameter than thediameter of the pipe or casing to define an annular space contiguous tothe cracked or perforated area. Aqueous solutions of amide polymerpolyaldehyde and hypohalite salt are preferably introduced rapidly underpressure through separate pipes in the proper proportions and at theproper alkalinity into the annular space where mixing occurs and themixture is forced by pressure through the cracked or perforated area andinto any porosities in the surrounding medium. When a sharp rise in backpressure is detected which indicates that gelation is occurring in theavailable porosities, pumping is discontinued and the packer is deflatedand removed. Alternatively, one of the solutions employed above may be asolution of an amide polymer and polyaldehyde adjusted to an acidic pHin the range of 4 to 5 while the second solution consists of thehypohalite salt dissolved in an aqueous alkaline reagent such as asolution of sodium hydroxide or trisodium phosphate.

The following examples illustrate the invention but are not to beconstrued as limiting its scope. All parts and percentages are by weightunless otherwise indicated.

EXAMPLE 1

An aqueous solution containing ˜20 percent of a homopolymer ofacrylamide is prepared and found to have a pH of about 5 and a viscosityof ˜475 centipoises at 27° C. as determined with a Brookfield LVTviscometer using a #2 spindle at 30 rpm. To 25 grams of the foregoingsolution is added with stirring 0.2 ml of a 40% solution of glyoxal inwater. To this solution at 21° C. is added with mixing a second solutionconsisting of 17 g of deionized water, 0.425 g of Na₃ PO₄.12H₂ O and 8 gof 5.25% aqueous solution of NaOCl. The resulting mixture has an initialpH of about 11.5 and forms a firm, non-pourable, water-insoluble gel in˜19 seconds. The gel is self-supporting and does not exude water onstanding. The gel is immersed in 5 N NaOH for several days without anynoticeable deterioration.

When the gelable composition of this example is placed in a poroussubterranean structure and gelled by the foregoing procedure, thestructure is rendered impermeable to the passage of aqueous liquid.

For purposes of comparison, a gel is prepared according to the foregoingprocedure except that no NaOCl is employed. While a non-pourable gel isformed by this procedure within about 15 seconds, the gel is entirelydestroyed when immersed in 5 N NaOH for about one hour.

EXAMPLE 2

An aqueous solution containing ˜20 percent of a homopolymer ofacrylamide is prepared and found to have a pH of 4.9 and a viscosity of388 centipoises at ˜25° C. as determined with a Brookfield LVTviscometer using a #2 spindle at 60 rpm. To a 40 g-portion of thissolution is added with stirring an amount of a 40% solution of glyoxalin water as specified in Table I. To the resulting stirred solution isadded with mixing a 40-g portion of a second solution containing 0.4 gof Na₃ PO₄, an amount of 5.25% active sodium hypochlorite aqueoussolution as specified in Table I and a remaining amount of water. Theresulting mixture has an initial pH of ˜11 and forms a firm,non-pourable, water-insoluble gel in the time specified in Table I. Thegel does not dissolve or otherwise deteriorate significantly when it isimmersed in 5 N NaOH for 17 days. The foregoing procedure is repeatedseveral times using various amounts of glyoxal and sodium hypohalite asspecified in Table I. In each instance, a firm, non-pourable gel isformed which exhibits considerable alkaline stability.

                                      TABLE I                                     __________________________________________________________________________    Amount of Glyoxal.sup.(1)                                                                       Amount of Sodium Hypochlorite.sup.(2)                                 mmoles of       mmoles of                                                                             Gel Alkaline                                Sample                                                                            ml of 40%                                                                           glyoxal/-                                                                             g of 5.25%                                                                            hypochlorite/-                                                                        Time,                                                                             Stabil-                                 No. solution                                                                            mole of amide                                                                         active solution                                                                       mole of amide                                                                         sec.                                                                              ity.sup.(3)                             __________________________________________________________________________    1   0.16   9.9    6.4     40.5    20-22                                                                             G                                       2   "     "       9.6     60.7    22-25                                                                             VG                                      3   "     "       12.8    81.0    20-25                                                                             E                                       4   0.24  14.9    6.4     40.5    17-19                                                                             G                                       5   "     "       9.6     60.7    15-18                                                                             VG                                      6   "     "       12.8    81.0    18-20                                                                             E                                       7   0.32  19.8    6.4     40.5    18.-20                                                                            G                                       8   "     "       9.6     60.7    15-19                                                                             VG                                      9   "     "       12.8    81.0    18-20                                                                             E                                       __________________________________________________________________________     .sup.(1) Amount of glyoxal is given in milliliters of 40% aqueous solutio     of glyoxal as well as millimoles of glyoxal per mole of amide moiety of       the polyacrylamide.                                                           .sup.(2) Amount of sodium hypochlorite is given in grams of 5.25% active      aqueous solution of sodium hypochlorite as well as millimoles of              hypochlorite per mole of amide moiety of the polyacrylamide.                  .sup.(3) In defining alkaline stability, one volume of the gel is placed      in 1.5 volumes of 5N NaOH for 17 days and then observed and rated as          follows: Ggel absorbs up to ˜90% of NaOH but remains as a firm,         insoluble gel; VGgel absorbs up to ˜75% NaOH but remains as a firm,     insoluble gel; Egel absorbs less than ˜50% NaOH and remains as a        firm, insoluble gel.                                                     

EXAMPLE 3

A packing device is positioned in a sewer wherein a large eroded crackhas developed where the seal between two sections of pipe has failed.The device has inflatable collars at either end of a rigid cylinderhaving a diameter sufficiently smaller than the sewer pipe to enable thedevice to be maneuvered into the desired position by cables. The rigidcylinder carries dual piping which connects to nozzles positioned in theannular space between the cylinder and the sewer pipe and directed sothat streams of fluid issuing from the nozzles will impinge on eachother and mix together. The piping is connected to pressure hoses whichare carried back through a manhole and connected to the outputs ofpositive displacement metering pumps. At least one of said outputs isfitted with a pressure gauge. The input end of one pump is connected toa first tank containing a known weight of an aqueous solution containing20 percent of a polyacrylamide similar to that of Example 1 above. ThepH of this solution is adjusted to 5 by addition of concentrated H₂ SO₄.This solution is characterized by a viscosity of 450 cps (BrookfieldLVT, #2 spindle, 30 rpm, 27° C.) and has been treated with a smallamount of sodium sulfite to react out most of the residual acrylamidemonomer and with an antimicrobial amount of sodium pentachlorophenate toprotect against mold growth. To said solution there is admixed about 0.8part of an aqueous solution containing 40 percent glyoxal for each 100parts of the polyacrylamide solution. No gelation occurs at thepredetermined pH of about 5 for the mixture when it is maintained atroom temperature for relatively short periods, e.g., one to two weeks.

The input end of the second pump is connected to a second tankcontaining an aqueous solution of 1.5 percent of trisodium phosphate and1.7 percent of NaOCl such that the pH of this solution is 12.3. Theamount of solution in the second tank is approximately equal in volumeto the aqueous solution in the first tank. The pumps are calibrated sothat they deliver equal volumes in equal times. When a test sample ofsolution from the first tank is mixed with an equal volume of thesolution from the second tank it is found that the resulting mixtureforms a non-pourable gel in less than about 40 seconds.

The packing device is positioned so that one of the collars is on eitherside of the crack in the sewer and the collars are inflated to form apositive pressure seal against the interior of the sewer pipe.The pumpsare started so that the polymer-dialdehyde solution and the trisodiumphosphate-sodium hypochlorite solution are mixed in the annular space ofthe packing device and the resulting mixture forced into and through thecracks into the surrounding medium. When the pressure gauge shows asharp rise in pressure the pumps are disconnected and the packing devicedeflated and removed from the sewer. On subsequent inspection it isfound that the cracked area is filled and covered with a firm adherentaqueous polymer gel.

In cases where a highly porous formation or void exists outside acracked or perforated sewer pipe or well casing it is generallydesirable to first introduce a more dilute solution containing from 2 to10 percent of amide polymer together with a correspondingly decreasedproportion of polyaldehyde, hypohalite salt and relatively strong baseso that the gelable composition may be pumped into the porosities orvoids more readily. In such cases it is usually desirable to increasethe concentration of amide polymer and proportion of polyaldehyde andhypohalite salt toward the end of the treatment in order to assure thedesired structural integrity in the final seal.

In instances wherein it is desirable to have a noticeable delay betweenthe time when the amide polymer, the dialdehyde, hypohalite salt and thealkaline agent are contacted and the time in which the gel reactionoccurs, it is desirable to reduce the alkalinity of the mixed solutionssuch that the pH of such solution is at a value between about 8 to about11, preferably from about 9 to about 10. At the lower values of pH inthe aforementioned ranges, the time between initial contacting of thereactants and gelation (while it depends significantly on theconcentration of the reactants) will generally vary from minutes toabout 48 hours. In contrast, at the higher levels of pH, gelation occursat times from about 5 to about 30 seconds.

What is claimed is:
 1. A method for rendering a porous structureimpermeable which comprises treating the porous structure with a gelableaqueous reaction mixture comprising an aqueous medium having dispersedtherein a water-soluble polymer derived from an ethylenicallyunsaturated amide, an aliphatic polyaldehyde and a metal salt of ahypohalite in proportions such that, at an effective reactiontemperature and an alkaline pH from about 8 to about 13.5, the reactionmixture upon being forced into and over the porosities of the structurereacts to form a gel capable of rendering said structure impermeable tothe passage of aqueous liquids.
 2. The method of claim 1 wherein thegelable reaction mixture is prepared by mixing in an aqueous medium thepolyaldehyde with amide polymer, an alkali metal hypohalite at a pH fromabout 8 to 13.5 in or immediately adjacent to said porosities.
 3. Themethod of claim 2 wherein the reaction mixture has an initial pH fromabout 10 to about
 13. 4. The method of claim 1 wherein the amide polymeris a homopolymer or copolymer of acrylamide.
 5. The method according toclaim 1 wherein the polyaldehyde is a dialdehyde.
 6. The method of claim5 wherein the dialdehyde is glyoxal.
 7. The method of claim 2 whereinthe alkali metal hypohalite is sodium hypochlorite.
 8. A gelable aqueousreaction mixture comprising an aqueous medium having dispersed therein awater-soluble polymer derived from an ethylenically unsaturated amide,an aliphatic polyaldehyde and a metal salt of a hypohalite inproportions such that, at an effective reaction temperature and analkaline pH from about 8 to about 13.5, the reaction mixture reacts toform a water-insoluble gel.
 9. The mixture of claim 8 wherein the amidepolymer is a homopolymer or copolymer of acrylamide, the polyaldehyde isglyoxal and the hypohalite salt is sodium hypochlorite.
 10. The gel ofclaim
 8. 11. The method of claim 4 wherein the polymer has a molecularweight such that an aqueous solution containing 40 weight percent of thepolymer has a viscosity in the range from about 50 to about 15,000centipoises as determined by a Brookfield LVT viscometer (#2 spindle, 15rpm and 25° C.).
 12. The method of claim 1 wherein the polymer has amolecular weight such that an aqueous solution containing 20 weightpercent of the polymer has a viscosity in the range from about 100 toabout 15,000 centipoises as determined by a Brookfield LVT viscometer(#2 spindle, 15 rpm and 25° C.).
 13. The reaction mixture of claim 9wherein the polymer has a molecular weight such that an aqueous solutioncontaining 40 weight percent of the polymer has a viscosity in the rangefrom about 50 to about 15,000 centipoises as determined by a BrookfieldLVT viscometer (#2 spindle, 15 rpm and 25° C.).
 14. The reaction mixtureof claim 8 wherein the polymer has a molecular weight such that anaqueous solution containing 20 weight percent of the polymer has aviscosity in the range from about 100 to about 15,000 centipoises asdetermined by a Brookfield LVT viscometer (#2 spindle, 15 rpm and 25°C.).
 15. The method of claim 1 wherein the polymer contains from about50 to 100 mole percent of one or more ethylenically unsaturatedcarboxamide monomers.
 16. The method of claim 1 wherein the polymercontains from about 90 to 100 mole percent of acrylamide, thepolyaldehyde is glyoxal and the hypohalite salt is sodium hypohalite.17. The method of claim 1 wherein a solution of polymer and polyaldehydeand an alkaline hypohalite solution are introduced into the porousstructures via separate streams.